6. PROJECT SUMMARY/ABSTRACT The goal of this project is to dissect which mechanisms the B cell receptor (BCR) signaling network employs to govern life and death cellular functions in healthy B cells, determine how the BCR signaling network is remodeled in three types of cancer with abnormal BCR signaling, and then kill malignant B cells by identifying and targeting those mechanisms which are required for survival. A combination of technologies, including measurement of signaling in individual cells from primary human tissues by flow cytometry and computational modeling of the BCR signaling network, will be used to achieve this goal. Signal transduction plays a key role in the development of healthy immune cells, and remodeling of cell signaling mechanisms drives tumor cell proliferation and suppresses apoptosis, contributing to tumor survival despite intense therapy regimens. In B cell non-Hodgkin's lymphomas, signaling through the B cell antigen receptor might be especially likely to support malignant B cells, as BCR signaling normally controls survival, apoptosis, and proliferation throughout development and differentiation. The central hypothesis of this project is that abnormal BCR signaling is required for the survival of lymphoma B cells. I have previously shown that signaling in human cancer specimens can be mapped at the individual cell level by flow cytometry and used this technology to identify cancer-cell specific alteration of BCR signaling in primary human lymphoma specimens. Here, I propose to integrate this single cell signaling profile approach with measurements of the functional outcomes of signaling, including cell death, proliferation, and gene expression. The Specific Aims are to (I) identify BCR signaling mechanisms required for contrasting functions - apoptosis and proliferation - in five stages of healthy human B cells, (II) identify abnormal BCR signaling activity in three mature B cell lymphomas and determine unique signaling features of each disease, and (III) identify abnormal BCR signaling events that are required for survival of lymphoma B cells and target these events to specifically kill lymphoma cells This project will advance cancer research by first clarifying our understanding of how signal transduction normally governs cell behavior and then by translating this mechanistic insight into a sharp understanding of critical 'targets of opportunity' in the signaling networks of malignant B cells.